the nasa officials warn the u.s. and the rest of the world simply do not have the ability to demany small meet tears, one in small quotations like the one that injured a thousand people in russia. or the one that now close to san francisco. nasa says it needs money to detect small asteroids that are flying around in space before they hit us and this is why. >> there are some objects we know that are coming years in advance. there are other objects still big enough to cause damage, that we only know about weeks in advance or days in advance. obviously we need to improve the capability to give us a large amount of notice, enough notice to mount a deflection mission, if we see one on a collision course. jenna: chief astronomer derek pitts is with us. so, derek, how vulnerable are we? >> well the real, the reality of it, jenna, is that while there are some large objects out there, we know pretty well where the big ones are. it is the smaller ones that we really have to be concerned about but the truth is that your chance